Homework Help:
Electrochemistry; redox potential

I have to calculate the redox potential of this equation:
Cr2(SO4)3 + 4K2SO4 + 3J2 +7H2O <=> K2Cr2O7 + 6KJ +7H2SO4
I used the nernst equation to calculate the potentials of
2Cr(3+)+7H2O -> Cr2O7(2-) +14H(+) +6e(-) and
I2 +2e(-) ->2J(-)
which were -1.42V and 0.51V, all ion concentrations were 0.1

So you used the Nerst equation to calculate the half cell potentials? The Nerst equation is used to find the overall redox potential for the overall redox reaction, not half cell potential as implied here.

The standard half cell potentials for these half reactions are used (look up in a table) to calculate Eo, find the number of electrons transferred and use the 0.1 concentrations in the ions for the overall reaction.

Staff: Mentor

Interesting. J was iodine symbol up to around 1980, it is used this way in older books.

So you used the Nerst equation to calculate the half cell potentials? The Nerst equation is used to find the overall redox potential for the overall redox reaction, not half cell potential as implied here.

The standard half cell potentials for these half reactions are used (look up in a table) to calculate Eo, find the number of electrons transferred and use the 0.1 concentrations in the ions for the overall reaction.

Yes the J was typo, it should be I. Don´t know what was I thinking. Could you explain me, how the Eo is calculated, or what should I be looking for? Is the reaction standard potential calculated between the pair which actually exchanged electrons Cr(3+) and I2, or somehow between the chrome and iodide pairs.